CV axles (constant velocity axles, also called drive shafts or half shafts) transmit power from the transmission to the wheels in front-wheel-drive and all-wheel-drive vehicles. They have CV joints at each end that allow the axle to flex with suspension and steering movement. When CV joints fail, you get a distinct clicking sound when turning. Replacement is a moderate DIY job that takes 1 to 2 hours per side.
How CV Joints Fail
CV joints are sealed in rubber or plastic boots filled with grease. The boots flex with every suspension movement and eventually crack from age, ozone exposure, and contact with road debris. Once a boot tears, grease flings out as the axle rotates and water and grit get in. Without grease, the joint wears rapidly. The classic symptom is a clicking or popping noise when turning – usually noticeable when accelerating through a tight turn (in a parking lot, for example). The clicking comes from the side that turned outward (e.g., right CV when turning left).
Inspection
Inspect CV boots at every service. Look for cracks, splits, missing clamps, or grease splatter on the surrounding suspension components. A torn boot caught early can sometimes be replaced (just the boot) before the joint is damaged. By the time clicking is audible, the joint is usually beyond rebuild and needs replacement. Some vehicles use sealed CV joints that cannot be serviced – the boot is replaced as part of axle replacement.
Reman vs New Axles
You can either replace the entire axle (a new or remanufactured assembly comes with both inner and outer CV joints, boots, grease, and clamps already installed) or replace individual CV joints (cheaper but more involved). For most DIY projects, replacing the complete axle is faster and gives a known-good result. Remanufactured axles are often half the price of new and come with a warranty – quality varies, so buy from a reputable supplier (GSP, EMPI, or OEM-branded reman are usually fine).
Replacement Procedure
Loosen the axle nut on the wheel hub before raising the vehicle (the wheel needs to be on the ground for leverage – the nut is typically very tight, often 250 to 400 Nm). Raise the vehicle and remove the wheel. Disconnect the lower ball joint (or the strut from the knuckle) so the knuckle can swing free. Pull the outer CV stub out of the hub. Pry the inner CV out of the transmission – this usually releases with a sharp pull, sometimes you need to pry against the transmission case with a pry bar.
Slide the new axle into the transmission until the inner CV clip seats in the differential side gear (you should feel and hear a click). Pass the outer stub through the wheel hub. Reconnect the lower ball joint or strut. Refit and torque the axle nut to the specified value (often very high – check the manual). Refit the wheel. Repeat on the other side if both axles need replacement.
Common Mistakes
Failing to fit the inner CV all the way into the transmission – the axle then pops out under load and leaves you stranded. Reusing the old axle nut on torque-to-yield applications – the nut may not stay tight. Forgetting to refit the heat shield or other small components. Not torquing the axle nut to specification – too loose and the hub bearing fails, too tight and you damage the bearing.
AWD Vehicles
AWD vehicles have CV axles at both the front and rear. Replacement at the rear typically requires partially dropping the rear differential or removing the rear knuckle, depending on the vehicle. The procedure is more involved than front-wheel-drive but the basic principles are the same.
CV axle dimensions and torque values are vehicle-specific. MechanicMate offers PDF workshop manuals for over 960 models at mechanicmate.net/shop.
— MechanicMate . Questions or a second opinion? [email protected].